The purpose of this chapter is to review the main biological structures responsible for visual perception. After a description of the main structures of the eyeball, which include the cornea and lens in the front part, responsible for the deviation of light rays, as well as the iris and the pupil, the description of the retina (layers of retinal cells) is emphasized. The role and distribution of photoreceptors (rods and cones) on the retina are reported. The different types of responses to light stimulation are described, leading to the understanding of the notion of receptive fields. As well, the main characteristics of two types of ganglion cells, magno and parvo, are summarized. The main structures involved in the routing of nerve impulses from the eye to the cerebral cortex are reported, emphasizing the main pathways and the architecture of the visual cortex. The most common visual disorders are then listed, including the ones originating from refraction problems.